Near azeotropic mixture substitute

ABSTRACT

The present invention comprises a refrigerant mixture consisting of a first mole fraction of 1,1,1,2-tetrafluoroethane (R134a) and a second mole fraction of a component selected from the group consisting of a mixture of CHClFCF 3  (R124) and CH 3  CClF 2  (R142b); a mixture of CHF 2  CH 3  (R152a) and CHClFCF 3  (R124); a mixture of CHF 2  CH 3  (R152a) and CH 3  CClF 2  (R142b); and a mixture of CHClFCF 3  (R124), CH 3  CClF 2  (R142b) and CHF 2  CH 3  (R152a).

ORIGIN OF THE INVENTION

The invention described herein was made in the performance of work undera NASA contract, and is subject to the provisions of Public Law 96-517(35 USC 202) in which the Contractor has elected to retain title.

This is a continuation of application Ser. No. 07/672,947 filed on Mar.21, 1991, now abandoned, which is a continuation of Ser. No. 07/503,465filed on Mar. 23, 1990, now abandoned.

TECHNICAL FIELD

This invention relates to the field of refrigerants for air conditionersystems and more particularly to a replacement fordichlorodifluoromethane.

BACKGROUND ART

Chlorofluorocarbons (CFCs) have been used in refrigerators and airconditioners for many years. Dichlorodifluoromethane or refrigerant 12(R12) has been the refrigerant of choice for automotive air conditioningsystems ever since it was developed in 1930. The history of thisdevelopment is discussed in detail in "Development of ChlorofluorocarbonRefrigerants", by R. Downing, ASHRAE Transactions 90 pt. 2, pp. 481-91,1984. R12 is widely used in automobiles because it is non-flammable, lowin toxicity, and compatible with the lubricants used in automotive airconditioning systems. Moreover it has the right combination of physicalproperties, such as boiling point and vapor pressure, to permitefficient use in these systems. However, over the years, large amountsof R12 have been released into the atmosphere as a result of damaged,leaky, or abandoned air conditioners as well as routine maintenance onthese devices.

In 1974, it was postulated that chlorofluoromethanes as well as otherchlorofluorocarbons are damaging to the earth's ozone layer. Thisresearch was reported in "Stratospheric SInk for Chlorofluoromethanes:Chlorine atom catalyzed Destruction of Ozone" by M. J. Molina and F. S.Rowland, Nature, 249:810-12, 1974. This theory has been confirmedrecently by the discovery of ozone "holes" over the Arctic andAntarctic. Richard A. Kerr reported in Research News, pp. 1489-92, Mar.25, 1988, that the ozone layer over latitudes corresponding to theUnited States has reduced about 5%.

The ozone layer acts as a barrier to UV radiation from the sun. Since UVradiation damages living organisms, destruction of the ozone layer wouldhave a serious impact on life on this planet. In fact there is strongevidence that human skin cancer rates are on the rise and thatphytoplankton in the ocean have been reduced by 25%.

This has resulted in a world-wide effort to eliminate release of ozonedepleting CFCs into the atmosphere, culminating in Montreal in 1987 inthe signing of an international agreement. The "Montreal Protocol" setsup a world-wide process to reduce production and consumption ofmaterials that can damage the ozone layer. In response to thisagreement, the aerosol, industrial cleaning and foam insulationindustries are starting to use alternatives to CFCs. There was report ofa proposal to ban automotive air conditioners in the Los Angeles Timeson Jul. 18, 1989.

The ideal replacement refrigerant would be a single compound: failingthat an azeotropic or near-azeotropic mixture would work. An azeotropeis a mixture whose composition and physical properties remain constantwith evaporation. A near-azeotrope is a mixture whose composition andphysical properties remain nearly constant with evaporation. Whileseveral investigators have researched replacements for automotive airconditioner refrigerants, the best replacements so far,1,1,1,2-tetrafluoroethane (R134a) and a blend covered by U.S. Pat. No.4,810,403, suffer from serious deficiencies. Since R134 a contains nochlorine, is not compatible with the lubricants used in presentautomotive air conditioners. Although the patented blend is compatiblewith such lubricants, it is not azeotropic and thus refrigerant leakscould substantially change its pressure characteristics.

If a near-azeotropic refrigerant mixture could be found that wasnon-flammable, low in toxicity, compatible with the lubricants used inautomotive air conditioning systems, had the right combination ofphysical properties, such as boiling point and vapor pressure, to permitefficient use in these systems, and was less damaging to the Earth'sozone layer it would satisfy a long felt need in the field of automotiveair conditioning technology. Use of this refrigerant would eliminateatmospheric damage caused by automotive air conditioners, ensurecompliance of automotive air conditioner systems with internationalagreements and thus eliminate the need to ban such air conditioners.

STATEMENT OF THE INVENTION

The present invention is directed towards a refrigerant mixturecomprising essentially two halocarbon components. The first halocarboncomponent and the second halocarbon component are present in essentiallynear azeotropic proportions which is approximately equal to the firsthalocarbon component being present in a mole fraction of about 0.5 toless than 1.0 while the second halocarbon component is present in a molefraction of about more than 0.0 to about 0.5. In the most preferredembodiment, the first halocarbon component is present in a mole fractionof about 0.7 to less than 1.0 while the second halocarbon component ispresent in a mole fraction of about more than 0.0 to about 0.3. Thefirst halocarbon component is CH₂ FCF₃ (R134a). The second halocarboncomponent can be CHClFCF₃ (R124), CH₃ CClF₂ (R142b), a mixture ofCHClFCF₃ and CH₃ CClF₂, a mixture of CHF₂ CH₃ (R152a) and CHClFCF₃, amixture of CHF₂ CH₃ and CH₃ CClF₂ , or a mixture of CHClFCF₃, CH₃ CClF₂and CHF₂ CH₃.

The resulting refrigerant has a vapor pressure close to that of CF₂ Cl₂,a nearly constant vapor pressure with evaporation, and is substantiallyless damaging to the earth's ozone layer than CF₂ Cl₂.

The preferred embodiment of this invention comprises about 0.5 (morepreferably about 0.7) to less than 1.0 mole fraction CH₂ FCF₃, and morethan 0.0 to about 0.5 (more preferably about 0.3) mole fraction of amixture of CHClFCF₃ and CH₃ CClF₂.

The most preferred embodiment of this invention comprises about 0.5(more preferably about 0.7) to less than 1.0 mole fraction CH₂ FCF₃ andmore than 0.0 to about 0.5 (more preferably about 0.3) mole fraction CH₃CClF₂.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows vapor pressure curves for the binary mixture of R134a andR124 at 0° C.

FIG. 2 shows vapor pressure curves for the binary mixture of R134a andR142b at 0 degrees C.

FIG. 3 shows vapor pressure curves for the ternary mixture of R134a,R152a and R142b at 0 degrees C.

FIG. 4 shows vapor pressure curves for the ternary mixture of R134a,R152a and R124 at 0 degrees C.

FIG. 5 shows vapor pressure curves for the ternary mixture of R134a,R124 and R142b at 0 degrees C.

FIG. 6 shows vapor pressure curves for the quaternary mixture of R134a,R124, R142b and R152a at 0 degrees C. FIG. 6(a) represents 90% R134awhile FIG. 6(b) represents 80% R134a.

FIG. 7 shows the near-azeotropic vapor pressure leakage characteristicsfor a typical mixture (R134a and R124).

DESCRIPTION OF THE INVENTION

The present invention contains at least two halocarbons, one of which isR134a. This invention comprises the mixtures shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Mixture  Component A    Component B                                           ______________________________________                                        1        R134a          R124                                                  2        R134a          R124b                                                 3        R134a          R124 + R142b                                          4        R134a          R152A + R124                                          5        R134a          R152a + R142b                                         6        R134a          R124 + R142b + R152a                                  ______________________________________                                    

Component A is present in the mixtures in a mole fraction of from about0.5 (more preferably about 0.7) to less than 1.0 while Component B ispresent in the mixtures in a mole fraction of from more than 0.0 toabout 0.5 (more preferably about 0.3). These mixtures were developed byreviewing the available literature to select components that have aboiling point in the range of -82 degrees C. and -5 degrees C., lowtoxicity, low ozone damage potential and low flammability, and testingto confirm that they were in fact near-azeotropic. To ensurecompatibility with compressor lubricants, each mixture was formulated tocontain at least one chlorinated compound.

A summary of literature data for the components of these mixtures isshown in Table 2. For comparison purposes, the literature data for R12is also shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Boiling      Vapor    Ozone           Flamma-                                 point        Pressure damage          bility                                  (degrees     (psia)@  poten-   Toxicity                                                                             (vol %                                  C.)          0 deg. C.                                                                              tial*    (in ppm)                                                                             in air)                                 ______________________________________                                        R134a -26.5      42.47    0      1000   None                                  R124  -12        32.72    <0.05  NA     None                                  R142b -9.7       NA       <0.05  1000   6.7-14.9                              R152a -25        NA       0      1000   3.9-16.9                              R12   -29.8      44.7     1      1000   None                                  ______________________________________                                         *compared to R12.                                                        

To test for azeotropic properties, various binary, ternary andquaternary mixtures were measured for vapor pressure at a constanttemperature of 0 degrees C. The results of these tests are summarized inFIGS. 1 through 6. It can be seen from the Figures that the vaporpressure of each mixture averages around 40 psia, which is close to thevapor pressure of R12. Further the vapor pressure of each mixture varieslittle with composition.

All of the above data suggest that each embodiment shown in Table 1 isnear-azeotropic, non-flammable, non-toxic, and compatible with airconditioner lubricants while being at least 67 times less damaging tothe ozone layer than R12. Thus any of the mixtures of Table 1 can beused as a direct replacement for R12.

The research has shown that mixture 3 of Table 1 is the preferredembodiment of this invention and mixture 2 of Table 1 is the mostpreferred embodiment of this invention because R142b has the highestsolubility in present refrigeration lubricating oils. Thenear-azeotropic leakage characteristics of a typical mixture (R134a andR124) are shown in FIG. 7.

Although the present invention has been described in detail withreference to particular preferred embodiments, persons possessingordinary skill in the art to which this invention pertains willappreciate that various modifications and enhancements may be madewithout departing from the spirit and scope of the claims that follow.

    ______________________________________                                        LIST OF ABBREVIATIONS                                                         Number   Formula    Name                                                      ______________________________________                                        Chemicals                                                                     R12      CCl.sub.2 F.sub.2                                                                        Dichlorodifluoromethane                                   R134a    CH.sub.2 FCF.sub.3                                                                       1,1,1,2-Tetrafluoroethane                                 R124     CHClFCF.sub.3                                                                            2-Chloro-1,1,1,2-tetrafluoroethane                        R142b    CH.sub.3 CClF.sub.2                                                                      1-Chloro-l,l-difluoroethane                               R152a    CHF.sub.2 CH.sub.3                                                                       1,1-Difluoroethane                                        Other                                                                         ppm      parts per million                                                    psia     pounds per square inch, absolute                                     ASHRAE   American Society of Heating, Refrigerating and                                Air-Conditioning Engineers                                           ______________________________________                                    

I claim:
 1. A refrigerant consisting of a mixture of a first molefraction of about 0.8 to less than 1.0 of CH₂ FCF₃ and a second molefraction of more than 0.0 to about 0.2 of a component selected from thegroup consisting of:a mixture of CHClFCF₃ and CH₃ CClF₂ ; a mixture ofCHF₂ CH₃ and CHClFCF₃ ; a mixture of CHF₂ CH₃ and CH₃ CClF₂ ; and amixture of CHClFCF₃, CH₃ CClF₂ and CHF₂ CH₃.
 2. A method of formulatinga refrigerant comprising the steps of;providing a first mole fraction ofabout 0.8 to less than 1.0 of CH₂ FCF₃, and adding a second molefraction of more than 0.0 to about 0.2 of a halocarbon selected from thegroup consisting of: a mixture of CHClFCF₃ and CH₃ CClF₂ ; a mixture ofCHF₂ CH₃ and CHClFCF₃ ; a mixture of CHF₂ CH₃ and CH₃ CClF₂ ; and amixture of CHClFCF₃, CH₃ CClF₂ and CHF₂ CH₃ ; said refrigerantconsisting of said first and second mole fractions.
 3. A refrigerantconsisting of the ternary mixture of CH₂ FCF₃, CHF₂ CH₃ and CH₃ CClF₂defined by the triangular diagram of FIG. 3 and having the vaporpressures at 0 degrees C. shown therein.
 4. A refrigerant consisting ofthe ternary mixture of CH₂ FCF₃, CHF₂ CH₃ and CHClFCF₃ defined by thetriangular diagram of FIG. 4 and having the vapor pressures at 0 degreesC. shown therein.
 5. A refrigerant consisting of the ternary mixture ofCH₂ FCF₃, CHClFCF₃ and CH₃ CClF₂ defined by the triangular diagram ofFIG. 5 and having the vapor pressures at 0 degrees C. shown therein. 6.A refrigerant consisting of the quaternary mixture of CH₂ FCF₃,CHClFCF₃, CH₃ CClF₂ and CHF₂ CH₃ defined by the triangular diagram ofFIG. 6a and having the vapor pressures at 0 degrees C. shown therein,said diagram representing the case where CH₂ FCH₃ is about 90 molepercent.
 7. A refrigerant consisting of the quaternary mixture of CH₂FCF₃, CHClFCF₃, CH₃ CClF₂ and CHF₂ CH₃ defined by the triangular diagramof FIG. 6(b) and having the vapor pressures at 0 degrees C. showntherein, said diagram representing the case where CH₂ FCH₃ is about 80mole percent.